The new plan will cap typical DSL users at 150 gigabytes of data each month and U-Verse customers — who also subscribe to television and home phone services — to 250 gigabytes of data each month. AT&T customers will be charged an extra $10 for each 50 gigabytes of data they consume over the monthly limit.

AT&T is known for laying the hammer down on bandwidth hogs, a lesson the company learned after dealing with the same problem on its wireless network after the iPhone launched. It was one of the first wireless companies to impose caps on the amount of data iPhone and other smartphone users could download and upload in order to relieve some of the strain on its network.

But rather than dealing with a lot of data flying across the wireless network because of data-intensive applications like Pandora, this move is aimed at file-sharing “bandwidth hogs” that download and upload huge files on a regular basis. There is a huge number of websites — like The Pirate Bay and BitTorrent — that have massive communities that facilitate file-sharing activity. Those files can include the likes of movies, music and video games.

The typical customer uses around 18 gigabytes of data each month, according to AT&T. A typical 10-minute-long video on YouTube can range anywhere from 10 to 50 megabytes, depending on the quality, while most songs range from 4 to 10 megabytes in size. If those figures are correct, it’s a pretty generous cap.

But with the emergence of cloud services, such as online storage provider Dropbox and Netflix’s increasingly popular streaming video service, that cap will start to seem smaller and smaller. Dropbox, for example, automatically synchronizes files on a computer and on a remote server. All that happens in the background and is usually an afterthought — but it could now easily be a liability.

AT&T is also an investor in streaming video games service OnLive, which is also a bit of a bandwidth hog. OnLive is becoming increasingly popular among casual PC users because it lets them play graphically demanding games on weak computers. Network congestion doesn’t seem like that much of an issue for broadband users right now. But AT&T is apparently preparing for a cloud revolution — when most services are run on remote servers with a lot of computing firepower — that is going to demand a lot of data.